In the art of data display, workers tend to categorize displays into "analog" and "digital" types. An "analog" display is exemplified by a meter needle (a pointer, e.g., on a d'Arsonval galvanometer) or by the position of a movable element, such as a column of mercury, in a thermometer.
On the other hand, a "digital" display is represented by alpha-numeric symbology, with a change in information content being represented merely by a change in the symbology (e.g., numbers displayed in a given field); as opposed to a change in position, color, etc. for the analog case.
There is presently a need in the art for analog displays which coact with digital input (i.e., respond to digital information input), principally because it is commonly convenient to gather and process information in digital form. There is also a need in the art for displays which render an analog presentation responsive to either digital or analog (electrical) input signals. The present invention is directed towards facilitating this.
This invention is directed towards providing such an analog display of electrical signals and particularly, to do so using raised-cathode gas discharge (RCG) display devices, especially as represented in a "bargraph" display. Such might be characterized as a "digitally-formulated" analog display.
As workers know, a bar type display may be characterized as an indicating device where the length or height of the indicating medium is proportional to the magnitude of the measured quantity. For example, a mercurial thermometer is a simple form of a bar type display, the height of the column of mercury being proportional to the temperature. Bar type display devices have potentially wide application in industrial process controls, aircraft instrumentation and, in general, in systems which require the mounting of a large number of displays on a relatively small instrument panel. To be useful in many of the potential applications, such display devices must be capable of responding rapidly to digital input signals, must occupy a minimum amount of space and must operate under a wide variety of environmental conditions.
Electro-mechanical devices for providing bar type displays are well known to the art, but these devices generally have the disadvantages of slow response time, of being relatively bulky and of limited accuracy when subjected to shock and vibration, and consequently have found only limited acceptance as display devices. Electrical devices are also known for providing bar type displays. A bargraph display is often a more natural and acceptable display representation of a variable than a digital readout--particularly when one wishes to quickly scan a number of displays for "out-of-range" indications, presenting analog data with digital accuracy.
Two methods of operating bar graph displays--"stepping" and "direct drive"--will be described along with the advantages of each. "Direct drive" is discussed below and is the operative mode of the described bargraph display embodiment.
By contrast, in the "stepping" mode of operation, only one gas discharge exists at any one time between the common anode and any cathode bar segment. The discharge is initiated at the lower end at a separate cathode, the "reset cathode"; and, once so initiated, provides a supply of ionized and metastable atoms, having a relatively high density in the area of the cathode adjacent the reset cathode. The presence of ions and metastable atoms results in a considerable reduction in firing voltage for this adjacent cathode (the "phase-one" cathode). Because there are a number of such "phase-one" cathodes connected in parallel, such a reduction in firing voltage--for any electrode adjacent another bar-electrode which is "ON" (discharging-glow)--is essential to a "stepping" operation. With only three (or more, if desired) parallel-connected sets of cathodes, and a "reset cathode" to start the first discharge, a glow can be stepped from cathode to cathode with any limit in the number of cathode bars.
The present invention contemplates improved bargraph displays of the known gaseous discharge type wherein a "glow" is typically established at a reset cathode and then, by the glow transfer principle, transferred up a series of spaced bar-cathodes. These electrodes are arranged as a "ladder" and when viewed at normal range can readily be made to appear to merge into a continuous bar of controlled length corresponding to the number of "digital counts" represented by glowing bars.
Now, various workers in the art have addressed problems like these (e.g., see U.S. Pat. Nos. 3,258,644; 3,328,790; 3,343,155; 3,659,149; 3,689,912 and 3,824,581). For instance, it has been proposed to provide a display which converts electrical input signals, such as BCD (binary coded decimal) signals, and presents them in a visual analog display with the magnitude (and/or sense) of the signals being represented by "indicator position" within the field. The display field might, for example, comprise a rectilinear array of bars, or "bargraph," with all segments between the minimum analog value and the indicated value illuminated uniformly to simulate a solid bar. In some such arrangements, a numerical value is indicated by the activation of a particular luminous segment--one of many in an aligned, parallel array, the segments being preferably visually contiguous, identically shaped and activatable so as to be independently illuminated. Such segments visually indicate increasing position-encoded values along the array. This invention provides improved techniques for a "ladder" array of electrodes for a bargraph display.
Such a display may be driven by electric circuit means responsive to the input signals and adapted to select and illuminate a specific luminous segment corresponding to the encoded value--thus, signal magnitude is indicated by illumination of a segment along the "bar array." The present invention is adapted to improving such "bargraph" displays, especially where the arrayed indicator segments, comprise planar, raised gas discharge cathodes.
Of course, RCG display devices are, in themselves, well known. They are typically arranged to indicate alpha-numeric symbols by the illumination of cathode substrates which combine to form a display symbol. Such cathodes coact with a confronting anode (typically a transparent film on a faceplate) to selectively provide the desired illumination as a cold-cathode glow discharge. Usually the electrodes are mounted on a ceramic baseplate and packaged in an envelope provided with a transparent window, being hermetically sealed with an ionizable gas therein. Cathode glow patterns are viewed through the window as display information (e.g., see U.S. Pat. No. 3,675,066 to Armstrong, Schott and Warne, and U.S. Pat. No. 3,675,065 to Warne, describing typical structure, fabrication and operation of such devices--also see FIG. 14).
Typically such arrangements place the anode adjacent to the transparent faceplate (e.g., a transparent conductive tin-oxide coating thereon), while the opposing cathodes are mounted upon the envelope base and arranged to coact with their anode so as to be selectively illuminated. Such cathodes typically comprise conductor strips mounted on pins in the envelope base and coupled to electrical power to be selectively excited. The anode and cathode elements, together with other conventional associated parts (such as spacers, bases, mounting pins and fill tube) are mounted in an envelope which is sealed, evacuated and partly backfilled with an ionizable gas, such as a neon mixture known in the art. For excitation and display, electrical power signals are applied between an anode and one, or several, associated cathodes so that the gas around these cathodes is discharge-excited into visible luminescence, the glowing-cathode array thus forming the intended information symbol. The present invention is arranged to utilize such raised-cathode gas discharge technology in a novel form and especially to provide an improved "bargraph" display.